Voltage questions

[FarmerGene]

Hi guys just finished the tractor cab build installed extra front and back lights, heater core with a three speed fan,and a stereo. Just to keep a eye on the power I also installed a volt meter. With nothing on I have 14.5 to 14.9 volts, when I turn everything on it drops down to 13 volts. I guess my question is how low can this drop before it affects battery storage? I'm assuming that if it stays above 12.25 volts I should be OK is this correct?:confused2:

 

[shaley]

Is that with the engine RPM of at least 1200 or at idle?

 

[tcartwri]

Anything less than 12.7 and you've maxed out the alternator and you're drawing on the battery. You should put a meter across the battery to confirm that your gauge is reading properly.

 

[SPYDERLK]

Hi guys just finished the tractor cab build installed extra front and back lights, heater core with a three speed fan,and a stereo. Just to keep a eye on the power I also installed a volt meter. With nothing on I have 14.5 to 14.9 volts, when I turn everything on it drops down to 13 volts. I guess my question is how low can this drop before it affects battery storage? I'm assuming that if it stays above 12.25 volts I should be OK is this correct?:confused2:

Is your VM directly across the battery? 13 is marginal for charging, but what you have sounds OK. The only time I think youd have a sub standard charge is if you started it and ran everything the whole time. The 13V would never top off the battery and youd soon have a battery hovering in the 70-80% charge range. Lead acid batteries are much healthier when fully recharged after being drained a little by starting. But if you turned off some significant amount of your electric load either a few minutes during running or before stopping the tractor it would be a significantly better charge. Check your battery voltage with a multimeter immediately before starting the tractor after it has sat a while [a couple hrs]. If you see 12.8 your are real good. If you see 12.5 worry. If you see 12.25 I would be surprised if it cranked well -- and the battery wont last long.
larry

 

[PILOON]

In reality you should do a load analysis and be running, probably 75-80% of the alternator output, leaving the balance for charging.

75% is the standard for aircraft based on constant loads and it would make sense that same should apply to vehicles.

To do so you convert everything to amperage consumption and compare that to the alternator output.
volts X amps = watts, so a 24 watt bulb draws 2 amps @ 12 volts.

For that reason I prefer one halagen spot vs 2 sealed beams as an example.

Some rotating yellow beacons actually have 3 flood lite bulbs inside that really eat up the power and if you run 2 headlights plus 2 rear work lights and a heater , on many smaller tractors you are maxed out.
Some folks also have plow mounted floods.
For some reason I have noticed many tractors use only 25 or 35 amp alternators, and that's not a lot for a night time snow blower tractor operation, especially if your yard is smallish with short charging times.
Also remember your glow plugs and cold starting will really drain down your battery so you you need that charging margin.

 

[Transit]

The correct, safe charging voltage range is narrow, 13.7 to 14.4 volts. The greater the voltage the faster the battery will charge. Voltages more than 14.5 will charge the battery faster but at a cost in battery life. A high voltage over a long term will cause the battery to overheat and gas. The gassing is the water; H2O breaking down to H and O. a lot depends where the volt meter is connected. The best place is across the battery terminals. Be sure of clean contacts in the system, not just the battery cables, but also the wires on the alternator and leading to the voltage regulator. The regulators job is to have a constant voltage and that is influenced by poor connections.

 

[FarmerGene]

Is that with the engine RPM of at least 1200 or at idle?

That's at a idle, I can figure out the load with the lights 4 55 watt lights, the thing the I can't get a handle on is the fan for the heater and the windshield wiper the heater appears to have a large draw on the system.There is a good possibility that everthing would be on at times. The tractor has a 40 amp alternator and my flashers are LED so they add very little, I will verify the voltage across the battery terminals tomorrow. Thanks for the guidance fellas.:thumbsup:

 

[RPW]

Re-check at about 1200rpm as suggested. You'll probably see your voltage increase to about 14v.

good luck.

 

[FarmerGene]

Re-check at about 1200rpm as suggested. You'll probably see your voltage increase to about 14v.

good luck.

Here's a update fellas once my RPMs are above 1200 the meter reads 14v no mater what i turn on, looks like it will be a toasty winter:thumbsup:

 

[Soundguy]

i'd install a center 0 ammeter and see net current charge.

I'd also reccomend running the alt at no more than 80% rated load for steady state operation... that is for happy and long alt life.

soundguy